Project Summary Traditionally, cardiotoxic effects in patients undergoing anthracycline-based chemotherapy (Anth-bC) are attributed to cardiomyocyte injury due to DNA damage and altered mitochondrial bioenergetics leading to excess reactive oxygen species and cell death. As a result, most research and treatment strategies are directed towards preventing cardiomyocyte injury. Recently, evidence from our group demonstrates that cardiac fibrosis also contributes to left ventricular dysfunction and heart failure symptoms following Anth-bC and now we have evidence that doxorubicin (Dox, a widely used Anth-bC) has a direct effect on cardiac fibroblasts to produce excess collagen. This project focuses on a candidate underlying mechanism by which Dox promotes cardiac fibroblasts activation and fibrosis: a stress response known as cellular senescence. Cellular senescence is characterized by permanent arrest of cell proliferation, mitochondrial dysfunction and development of a senescence-associated secretory phenotype (SASP) producing inflammatory cytokines, chemokines and proteases with both autocrine and paracrine effects. Although senescence has been studied in multiple cell types, there are virtually no data on senescence in adult cardiac fibroblasts. We have now evidence that cardiac fibroblasts exposed to Dox indeed develop mitochondrial dysfunction and become prematurely senescent. However, even in well studied cell types a complete understanding of the SASP secretome and the exact nature of the relationship between mitochondrial dysfunction and the senescence phenotype remain unclear. We propose to use isolated adult rat cardiac fibroblasts and a clinically relevant rat model of cardiotoxicity to critically determine the role of the secretome constituents in the activation of cardiac fibroblasts and the role mitochondrial dysfunction in the development of senescence and its association to cardiac fibrosis and left ventricular dysfunction. Our specific aims are designed to answer the following questions: 1) What are the proteomic constituents of the cardiac fibroblast secretome induced by Dox that stimulate a pro-fibrotic phenotype; 2) is there a causal role for mitochondria dysfunction in the development of Dox-induced senescence and SASP?; and 3) to what extent cardiac fibroblasts senescence, SASP and mitochondrial dysfunction are associated with the establishment and progression of myocardial fibrosis and LV dysfunction in vivo. Through the accomplishment of these significant aims, this project will train the PI in new areas of mass spectrometry-based proteomics, mitochondrial function and senescence biology. This training includes workshops in proteomics, experiential learning and development of leadership skills. Ultimately, this will lead to the success of her long term goal of becoming an independent funded investigator significantly contributing to the understanding of the molecular and cellular causes of the cardiovascular toxicities of chemotherapeutics that can be targeted to prevent and/or mitigate cardiovascular morbidities induced by these therapies.